1. Field of the Invention
The embodiments of the invention generally relate to a method and apparatus for determining relative chamber positions in a semiconductor processing system.
2. Background of the Related Art
Semiconductor substrate processing is typically performed by subjecting a substrate to a plurality of sequential processes to create devices, conductors and insulators on the substrate. Each of these processes is generally performed in a process chamber configured to perform a single step of the production process. In order to efficiently complete the entire sequence of processing steps, a number of process chambers are typically coupled to a central transfer chamber that houses a robot to facilitate transfer of the substrate between the process chambers. A semiconductor processing platform having this configuration is generally known as a cluster tool, examples of which are the families of AKT PECVD, PRODUCER®, CENTURA® and ENDURA® processing platforms available from Applied Materials, Inc., of Santa Clara, Calif.
Generally, a cluster tool comprises a central transfer chamber having a robot disposed therein. The transfer chamber is generally surrounded by one or more process chambers. The process chambers are generally utilized to process the substrate, for example, performing various processing steps such as etching, physical vapor deposition, ion implantation, lithography and the like. The transfer chamber is sometimes coupled to a factory interface that houses a plurality of removable substrate storage cassettes, each of which houses a plurality of substrates. To facilitate transfer of a substrate between a vacuum environment of the transfer chamber and a generally ambient environment of the factory interface, a load lock chamber is disposed between the transfer chamber and the factory interface.
In flat panel processing, glass substrates such as those utilized to fabricate computer monitors, large screen televisions and displays for PDAs and cell phones and the like, are becoming dramatically larger as the demand for flat panels increases. For example, glass substrates utilized for flat panel fabrication have increased in area from 550 mm×650 mm to 1500 mm×1800 mm in just a few years, and are envisioned to exceed four square meters in the near future.
To accommodate processing such large area substrates, processing systems have also increased in size. For example, the internal diameter of a transfer chamber utilized to move such large substrates between processing chambers in a typical cluster tool has increased from about 80 to about 135 inches to accommodate the substrate size. The additional size and mass of the larger transfer chambers make these chambers more susceptible to deformation due to thermal effects. Chamber deformation may result in changes in position of the surrounding processing chambers relative to the center of the transfer chamber from which robotic motions during substrate transfer are referenced.
As the position of the processing chamber moves, the accuracy and repeatability of substrate placement during transfers between the transfer chamber and the processing chamber diminishes. In some cases, the accuracy and repeatability of substrate placement may exceed the substrate placement tolerances required to ensure good processing results and prevent substrate damage during transfer (e.g. due to misplacement of the substrate on either a substrate support within the processing chamber or on the robot's end effector when retrieving a substrate from the processing chamber). With the increased number of devices formed on large area substrates due to both increased device density and larger substrate areas, the value of each substrate has greatly increased. Accordingly, damage to the substrate or yield loss due to non-conformity because of substrate misalignment is highly undesirable.
The change in relative position between the processing and transfer chambers may be further aggravated as different processing chambers surrounding the transfer chamber change in temperature. For example, a processing chamber configured to perform a plasma enhanced chemical vapor deposition (PECVD) process may operate at a temperature of about 400 degrees Celsius, which may heat an adjoining facet of the transfer chamber to about 75 degrees Celsius. If the temperature of the PECVD processing chamber is decreased for service or other reasons, the reduced thermal load will cause the transfer chamber to contract, which may change the position and orientation of the facet relative the transfer chamber's centerline. Other facets positioned around the transfer chamber may be similarly affected.
In a steady state thermal condition, the relative positions between the processing chambers and transfer chambers are known, thereby allowing robot movement to be calibrated. However, changes in the thermal attributes of any of the chambers may cause the substrate exchange position in any chamber to move from its calibrated position, thereby greatly increasing the probability of substrate misalignment during transfers. An inaccurately positioned substrate is susceptible to damage during transfer and prevents repetitive device fabrication with low defect rates. Consequently, it would be beneficial to know or predict any change in relative position between chambers to ensure proper substrate placement.
Therefore, there is a need for an improved method and apparatus for determining a substrate exchange position to enable accurate and repeatable substrate transfers in cluster tools.